Aluminum alloy



Patented Jan. 30, 1934 UNITED STATES ALUMINUM ALLOY RolandSternen-Rainer, Heilbronn, Germany, assignor to American LurgiCorporation, New York, N. Y., a corporation of New York No Drawing.Application November 24, 1930., Serial No. 497,956, and in GermanyDecember 7 Claims.

My present invention comprises an improved cast, forged, drawn or rolledaluminum alloy with additions of magnesium and silicon andof a metal ofthe group consisting of manganese, nickel. cobalt, chromium, iron andtitanium, or a metal of the group antimony, cadmium and bismuth, or acombination of metals of these two groups. It is the object of myinvention to improve the physical properties of the cast, forged,drawnor rolled alloy.

Heretofore aluminum alloys containing copper and magnesium. have beenimproved by heat treatment. The improvement has been ascribed to thetendency of certain components, particularly copper-aluminum orcopper-magnesiumaluminum particles, to be thrown out of solution fromthe. aluminum during the aging after the heat treatment. 7

If the alloy is free from copper another element must be addedwhich.-with the aluminum and magnesium, is able to form mixed crystalsin order to render possible a technically valuable improvement of thephysical properties by heat treatment. For example, zinc is used as suchan element. Silicon is also known as an addition element, but it hasonly been possible to get a noticeable improvement of the properties ofsuch an alloy by so-called artificial aging, that is storing at atemperature over 100 C. On the other hand, it is known that someaddition elements are valueless ,for magnesium-containing aluminumalloys, as they combine with the magnesium to form a compound insolublein aluminum and so hinder the precipitation of particles from solution.Antimony is, for instance, such an element. It should be noted howeverthat antimony is a very valuable component for an aluminum alloy in sofar as the production of a non-corroding alloy is concerned. In suchcases, antimony forms non-corroding films.

I have now discovered that some combinations containing aluminum alloyswith additions of other elements both show the good qualities of anon-corrosive alloy and can be improved by heat treatment. Suchcombinations are primarily aluminum alloys with at least 0.1% to 6%'Inagnesium, 0.6% to 6% silicon and at least 0.2% to 10% of a metal ofthe group consisting of manganese, nickel, chromium, cobalt, iron andtitanium. It should here be noted that the alloy does not contain anysubstantial amount of copper other than as a possible impurity and that,nevertheless, it can be improved by a schedule of heat treatmenthereinafter described in detail.

' The improvement by heat treatment is due particularly to thesimultaneous presence of magnesium and silicon, but it is furtherstrengthened by the presence of one or more metals of the grouphereinbefore defined.

If, for instance, an alloy which has an approximate composition of 2%magnesium; 1 1% manganese, 96.6% aluminum (the aluminum containing thenormal impurities of, say, 0.3% to 0.4% iron and silicon) issand cast,it has a tensile strength of about 17 kg. per sq. mm. and an elongationof 3 to 5%. If this alloy is heated to a temperature of 570 C. andquenched, no improvement of the tensile strength is effected by aging atnormal temperature. Forged, drawn or rolled material, of the foregoingcomposition, has a tensile strength of about 22 kg. per sq. mm. and, ina state of plasticity, anelongation of 22 24%, and cannot be improvedeither by artificial or natural aging. On the contrary, if, inaccordance with my invention, the alloy has a composition which variesfrom the above by the addition of 0.6% silicon, so that the totalsilicon content amounts to 0.9%, and further such an alloy is heatedsome hours at a temperature of 570 C., quenched and aged at normal, thatis to say, room temperature for several days, then the tensilestrengthis increased to 23 kg. per sq. mm. for east alloys and to about 34 kg.per sq. mm. for rolled alloys. The elongation however is not altered.

To show, on the other hand, the importance of the manganese content, itmay be stated that a forged aluminum, alloy, containing only 0.75%silicon and 0.5% magnesium, which was heated at a temperature of about560 C., quenched and aged at room temperature for '7 days, had a tensilestrength of 22 kg./sq. mm. and an elongation of 30%. If about 1%manganese is further added and the alloy treated in the same manner byheating to 560 C., quenching and aging at room temperature for '7 days,it has a. tensile strength of about 32 kg. per sq. mm. and an elongationof about 24%.

It will be seen from these examples that neither the addition ofmagnesium and silicon alone,.nor the addition of magnesium and manganesealone, to aluminum, eifects any considerable improvement of the aluminumalloys by heating, quenching, and aging at room temperature, but onlythe simultaneous presence of magnesium, silicon and manganese.

Other metals, such as nickel, cobalt, chromium, iron or titanium, cannaturally be added instead of .manganese in proportions of 0.2% to 10%,either alone or combined, without depart Instead of a metal of the grouph ereinbeforev defined, or in addition thereto, a metal of the groupconsisting of antimony, cadmium and bismuth can be used in order tofurther improve the properties of the alloy, especially as regardsresistance to corrosion. The limit for the addition of antimony, cadmiumand bismuth is 5%, because the antimony forms an insoluble combinationwith the magnesium." Care should be taken that there is always moremagnesium present than corresponds to the stoicheometric amount requiredfor the combination withantimony, in order to form magnesiumsilicide,which dissolves in the solid state in the aluminum.

When an alloy with 2% magnesium, 1.4% manganese, 0.2% antimony, 0.9%silicon, remainder aluminum, is sand cast, it has a tensile strength ofabout 18 kg. per sq. mm. and an elongation of about 3 to 5%. If thisalloy is heated at about 570 C. for about three hours, quenched and agedat room temperature for at least 4 days, .the tensile strength amountsto 24 kg. per sq. mm. A further improvement is ob-' tained if theforged, drawn or rolled material, rather than the cast material, issubjected to the heat treatment. In this case, an alloy, comprisingabout 2% magnesium, 1.4% manganese, 0.2% antimony, 0.9% silicon,remainder aluminum, after heat treatment has a tensile strength of about35 kg. per sq. mm. and an elongation of about 22 to 24%.

In this specification and in the claims, .the terms heating and agingare intended to cover not only the specific temperatures enumeratedherein but also the known variations of these temperatures which arepermissible under various conditions known to those skilled in the arts.For example, it is known that heating of an alloy canbe carried out at alower temperature if the length of the heating step is correspondinglyincreased.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is,

1. An aluminum alloy substantially devoid or copper and composed of from0.8% to 6.0% of magnesium, from 0.6% to 6.0% of silicon, from 0.2% to 5%of at least one metal of the group consisting of manganese, nickel,cobalt, chromium, titanium and iron, and aluminum the remainder, saidalloy being further characterized by increased tensile strength withsimultaneous maintenance of' high resistance to corrosion by means of aheat treatment consisting of heat treating the alloy at a temperatureclosely below the solidification point, quenching and finally aging atroom temperature for a period of several days.

2. An aluminum alloy substantially devoid of copper and composed of from0.2% to 6.0% of magnesium, from 0.6% to 6.0% of silicon, from 0.2% to 5%of a metal of the group consisting of manganese, nickel, cobalt,chromium, titanium and iron, from 0.05% to 5.0% of a metal of the groupconsisting of antimony, cadmium and bismuth, and aluminum the remainder,said alloy being further characterized by increased tensile strengthwith simultaneous maintenance of high resistance to corrosion by meansof a heat treatment consisting of heat treating the alloy at atemperature closely below the solidfication point, quenching and finallyaging at room temperature for a period of several days.

3. An aluminum alloy improved in tensile strength by a treatmentconsisting of heating to incandescence, quenching and aging at roomtemperature for a period of several days, said alloy being characterizedby the following constitution: magnesium 2%; manganese 1.4%; silicon0.9%; antimony 0.2%; with aluminum the remainder.

4. An aluminum alloy improved in tensile strength by a treatmentconsisting of heating to incandescence, quenching and aging at roomtemperature for a period of several days, said alloy being characterizedby the following constitution: magnesium 0.5%; manganese 1.0%; 0.75%;with aluminum the remainder.

- 5. An aluminum alloy improved in tensile strength by a treatmentconsisting of heating to incandescence, quenching and aging at roomtemperature for a period of several days, said alloy being characterizedby the following constitution: magnesium 2.0%; manganese-1.4%; silicon0.9%;

with aluminum the remainder.

6. Method of improving the tensile strength and other physicalproperties of an aluminummagnesium-silicon alloy substantially devoid ofsilicon copper and containing magnesium within the range of from 0.2%to. 6.0%.and silicon within the range of from 0.6% to 6.0%, withaluminum the remainder, without destroying the capacity of that alloy tobe improved by a heat treatment which involves heat treating the alloyat a temperature closely below the solidification point, quenching andfinally aging at room temperature for a period of several days, whichmethod consists in alloying therewith from 0.2% to 5% of a metal of thearbitrary group consisting of manganese, nickel, cobalt, chromium,titanium and iron.

ganese, nickel, cobalt, chromium, titanium and iron, and from 0.05% to5.0% of a metal of the arbitrary group consisting of antimony, cadmiumand bismuth.

- ROLAND STERNER-RAINER.

'7. Method of improving the tensile strength and l

